Method for electrostatic image development employing toner and carrier supported by a conductive liquid electrode surface

ABSTRACT

A method and apparatus for developing an electrostatic latent image formed on an electrophotographic surface by contacting said surface with a liquid or dry type developer, said developer comprising two components, one component being toner particles and the other component being carrier particles for said toner particles. A conductive liquid functioning as a liquid development electrode is located in close proximity to the surface containing the latent image and the developer is floated on the surface of the development electrode, between said electrode and said surface.

O United States Patent 1 1 [111 3,865,611

Sato et al. Feb. 11, 1975 54] METHOD FOR ELECTROSTATIC IMAGE 3,068,115 12/1962 01111616611 117/37 LE ENT E PLOYING TONER AND 3,336,906 8/1967 Michalchik ll8/637 gixi g f g x BY A CONDUCTWE 3,406,062 10/1968 Michalchik 96/1 LY 3,438,904 4/1969 Wagner 252/621 LIQUID ELECTRODE SURFACE 3/1970 Witter 117/37 LE Inventors: Masamichi Sato; Osamu Fukushima,

both of Osaka, Japan Assignee: Xerox Corporation, Stamford,

Conn.

Filed: Nov. 9, 1972 Appl. No.: 305,017

U.S. Cl 1l7/17.5, 117/37 LE, 96/1 SD, 96/1 LY, 118/637, 1l8/DlG. 23

Int. Cl. ..G03g 13/08, 603g 13/10, gm Q Sg 15/08, greys/10 Field of Search 117/17.5, 37 LE; 96/1 R, 96/1 LY; 355/10; 1l8/DlG. 23, 637

References Cited UNITED STATES PATENTS 12/1960 Gundlach 252/62.l

Primary ExaminerMichael Sofocleous [57] ABSTRACT other component being carrier particles for said toner particles. A conductive liquid functioning as a liquid development electrode is located in close proximity to the surface containing the latent image and the developer is floated on the surface of the development electrode, between said electrode and said surface.

8 Claims, 2 Drawing Figures loz METHOD FOR ELECTROSTATIC IMAGE DEVELOPMENT EMPLOYING TONER AND CARRIER SUPPORTED BY A CONDUCTIVE LIQUID ELECTRODE SURFACE BACKGROUND AND SUMMARY OF THE INVENTION The present invention relates to a method and apparatus for the development of an electrostatic image wherein a two component developer is interposed between a conductive liquid functioning as a development electrode and the surface containing the electrostatic latent image.

It is well known that an electrostatic latent image formed on an electrophotographic surface can be developed by liquid development and by the use of a conductive liquid as a development electrode. In liquid development, the developer is in the form of a dielectric liquid vehicle having electrophoretic toner particles dispersed therein. Suitable conductive liquids which have been used as a development electrode include, for example, mercury, water or a polar organic solvent. In such a development process, a thin film of developer is formed between the conductive liquid and the latent image surface which enables the toner particles in said thin film of developer to contact the latent image. The thickness of the thin film of developer containing the toner particles varies according to the properties of the developer and the conductive liquid but generally is in the range of about several tens of microns or less, for example, about 30 microns. It has been noted that when the distance between the development electrode and the latent image becomes small, as indicated above, toner particles tend to stick to the background of the image, thereby causing fog in the image background. Reducing the concentration of toner particles in the developer does not solve the problem because the concentration of toner particles contained in the thin film between the development electrode and the latent image would also be reduced resulting in a very low development density and an inadequate image. To increase the development density, it would be necessary to increase the amount of toner particles contained in the thin film of developer, that is, to increase the toner particle construction in the developer. However, increasing the toner concentration would again cause a substantial increase of the fog in the background of the image.

In accordance with the present invention, the foregoing problems are overcome by interposing a developer between the surface of an electrostatic latent image and a conductive liquid functioning as a development electrode wherein said developer comprises two components, one component being toner particles and the other component being carrier particles for said toner particles, said carrier particles having a density less than that of the conductive liquid. Because the carrier particles have a lower density than the conductive liquid, the developer is floated on the surface of the conductive liquid thereby permitting the toner particles in the developer to reach the latent image. By utilizing the developer of the present invention, the thickness of the developer film interposed between the development electrode and the latent image can be increased to about several hundred microns to several millimeters, thereby producing a good image density with a substantial reduction in the image background fog.

The method for the development of an electrostatic latent image according to the present invention is applicable to both wet and dry-type development with the vehicle for the wet-type developer being a dielectric liquid and the vehicle for the dry-type developer being air. In both cases, the carrier particles are formed of a material that is not wetted by the conductive liquid.

In order to avoid the depletion of the developer while in contact with the electrostatic latent image, the developer can be continually circulated from a reservoir to the interface between the electrophotographic surface and the conductive liquid. As the developer accumulates on the surface of the conductive liquid, it overflows from said surface and is returned to the developer reservoir.

It is therefore an object of the present invention to provide a method and apparatus for the development of an electrostatic latent image using either a wet or dry-type developer interposed between the latent image surface and a liquid development electrode wherein the developer comprises two components, one component being toner particles and the other component being carrier particles for said toner particles.

Another object of the present invention is to provide a method and apparatus for the development of an electrostatic latent image wherein the carrier particles have a density less than that of the conductive liquid functioning as the liquid development electrode, so that the developer is floated on the surface of the conductive liquid thereby permitting the toner particles in the developer to reach the latent image.

A further object of the present invention is to provide a method and apparatus for the development of an electrostatic latent image wherein the developer is continuously circulated from a reservoir to the interface between the latent image surface and the development electrode and back to the reservoir.

Other objects and further scope of applicability of the present invention will become apparent from the detailed description given hereinafter; it should be understood, however, that the detailed description and specific examples, while indicating preferred embodiments of the invention, are given by way of illustration only, since various changes and modifications within the spirit and scope of the invention will become apparent to those skilled in the art from this detailed description.

BRIEF DESCRIPTION OF THE DRAWINGS The present invention will become more fully understood from the detailed description given hereinbelow and the accompanying drawings, which are given by way of illustration only and thus are not limitative of the present invention and wherein,

FIG. 1 is a sectional schematic illustration of an apparatus for developing an electrostatic latent image utilizing a conductive liquid as the developing electrode and a developer material; and

FIG. 2 is a sectional schematic illustration of an apparatus for developing an electrostatic image wherein the developer material is continually recycled.

DESCRIPTION OF THE PREFERRED EMBODIMENTS In the embodiment of the present invention shown in FIG. 1, a web-like electrophotographic material is driven around a drum 101, with the latent image being disposed on the outside surface of the web. The drum 101 extends into the upper portion of the receptacle or tank 104 and is supported for rotation in an elevated position above the bottom of said tank. The web-like material 100 is brought into contact with a developer 102 which is floated on the surface of a conductive liquid 103. In the case of a dry-type developer, such as for example a cascade developer, the developer 102 comprises, according to the present invention, two components, one component being toner particles and the other component being carrier particles for said toner particles. In the case where a wet-type developer is utilized, said developer comprises a dielectric liquid in which carrier particles containing said toner particles are dispersed.

Whether or not a dry type or wet type developer is used, it is necessary that the specific gravity of the carrier particles be less than that of the conductive liquid 103. When using a wet type developer, it is also important that the specific gravity of the dielectric developing liquid be less than that of the conductive liquid and that said liquids are immiscible with each other.

The carrier particles which can be used in the present invention are similar to carrier particles used in a cascade developer. Exemplary of the carrier particles which can be used when the conductive liquid is mercury, includes such materials as glass, plastic, ceramic materials and the like. If the conductive liquid is water or an aqueous solution, then the carrier particles can be a plastic material, for example polyethylene, hollow glass particles, plastic balls, and the like, having a specific gravity less than that of the conductive liquid. The size of the carrier particles is preferably about several tens of microns to several millimeters, for example about 30 microns to several millimeters. It is preferred that the carrier particles be hydrophobic when the conductive liquid is an aqueous solution, water or the like.

According to the present invention, a thin developer film having a thickness of several hundred microns to several millimeters is provided between the latent image surface and the conductive liquid.

FIG. 2 shows an embodiment of the present invention wherein the developer is continuously circulated. As shown in the drawing, the development apparatus comprises an outer tank 203 and an inner tank 104 positioned inside the confines of the outer tank and supported in an elevated position above the bottom of the outer tank. The space in tank 203 below the bottom of innter tank 104 is adapted to contain a reservoir of developer 102. The inner tank 104 is substantially filled with a body of conductive liquid 103 and the developer 102 is interposed between the conductive liquid and the surface of the electrostatic latent image. The drum 101 is positioned to be partially immersed in the contents of the inner tank 104 and is supported for rotation through the development apparatus. Any electrostatic latent image present on the photoconductive surface of the web 100 is exposed to the developer 102, and by the combined action of the force of the electrostatic image and the conductive liquid 103 functioning as a developing electrode, the latent image on web 100 is developed. As the drum is rotated the developer is supplied from the left side of tank 104 along an inclined plate 201 and is carried to the right side of said tank due to the rotation of the drum. When tank 104 becomes filled, developer overflows from the right upper corner of the tank and is collected in the bottom portion of the developer tank 203 via an inclined path 202. The developer can then be returned to the original inclined plate by any suitable device depending on whether the developer is of the liquid or dry type. A suitable quantity of conductive liquid is provided in container 104 so that it does not overflow from said container.

According to the present invention, by the use of a two component developer, one component being toner particles and the other component being carrier particles for said toner particles, a space of several hundred microns to several millimeters can be maintained between the conductive liquid electrode and the latent image. Thus an image with sufficient contrast is obtained because it contains less background fog and more toner particles than images obtained through the use of thin development films of several tens of microns or less.

The invention being thus described, it will be obvious to one skilled in the art that the same may be varied in many ways. Such variations are not to be regarded as departures from the spirit and scope of the invention, and all modifications as are embraced by the appended claims are intended to be included within the purview of the present invention.

What is claimed is:

1. In the process of developing an electrostatic latent image by contacting the surface of a latent image carrier with a developer therefor, locating a body of conductive liquid functioning as a liquid development electrode closely adjacent said surface, and interposing the developer between said surface and said electrode; the improvement wherein said developer contains two components, one component being toner particles and the other component being carrier particles for said toner particles, said carrier particles being formed of a material that is not wetted by said conductive liquid and having a density less than that of said conductive liquid, whereby said developer is floated on the surface of said conductive liquid.

2. In the process as set forth in claim 1, whereby the developer is floating on the surface of the conductive liquid in a vehicle, the vehicle for said developer being air.

3. In the process as set forth in claim 1, whereby the developer is floating on the surface of the conductive liquid in a vehicle, the vehicle for said developer being a dielectric liquid.

4. In the process as set forth in claim 1, the developer interposed between the conductive liquid and the latent image has a thickness of about several hundred microns to several millimeters.

5. In the process as set forth in claim 1, the conductive liquid is selected from the group consisting of mercury, an aqueous solution or water.

6. In the process as set forth in claim 1, where the conductive liquid is mercury, the carrier particles are selected from the group consisting of glass particles, plastic particles or ceramic particles.

7. In the process as set forth in claim 1, where the conductive liquid is water or an aqueous solution, the carrier particles are selected from the group consisting of polyethylene particles, hollow glass particles or plastic balls.

0. In the process as set forth in claim 1, the size of the carrier particle is about several tens of microns to sev- UNITED STATES PATENT AND TRADEMARK OFFICE CERTIFICATE OF CORRECTION PATENT NO. 3,865,611

D D 1 February 11, 1975 INVENTO I Masamichi Sato and Osamu Fukushima It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

On the cover page, following the word "Assigneez" kindly delete "Xerox Corporation, Stamford, Conn." and substitute therefor --Rank Xerox, Ltd., London, England-.

Column 4, line 33, Claim 1, the word "contains" should read -comprises.

Signed and Scaled this twenty-sixth ,D ay Of A ugust 1 9 75 [SEAL] A ttes t:

RUTH C. MASON C. MARSHALL DANN Arresting Officer Commissioner oj'larents and Trademarks UNITED STATES PATENT AND TRADEMARK OFFICE CERTIFICATE OF CORRECTEQN PATENT NO. 1 3,865,611

DATED 1 February ll, 1975 V 0 I Masamichi Sato and Osamu Fukushima It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

On the cover page, following the word "Assigneez" kindly delete "Xerox Corporation, Stamford, Conn." and substitute therefor --Rank Xerox, Ltd. London, England-.

Column 4, line 33, Claim 1, the word "contains" should read -comprises-.

Signed and Scaled this twenty-sixth I) 3} of A ugust 19 75 [SEAL] A ttest:

RUTH C. MASON C. MARSHALL DANN Arresting Officer (mnmissl'oner uflarenls and Trademarks 

1. IN THE PROCESS OF DEVELOPING AN ELECTROSTATIC LATENT IMAGE BY CONTACTING THE SURFACE OF A LATENT IMAGE CARRIER WITH A DEVELOPER THEREFOR, LOCATING A BODY OF CONDUCTIVE LIQUID FUNCTIONING AS A LIQUID DEVELOPMENT ELECTRODE CLOSELY ADJACENT SAID SURFACE, AND INTERPOSING THE DEVELOPER BETWEEN SAID SURFACE AND SAID ELECTRODE, THE IMPROVEMENT WHEREIN SAID DEVELOPER CONTAINS TWO COMPONENTS, ONE COMPONENT BEING TONER PARTICLES AND THE OTHER COMPONENT BEING CARRIER PARTICLES FOR SAID TONER PARTICLES, SAID CARRIER PARTICLES BEING FORMED OF A MATERIAL THAT IS NOT WETTED BY SAID CONDUCTIVE LIQUID AND HAVING A DENSITY LESS THAN THAT OF SAID CONDUCTIVE LIQUID, WHEREBY SAID DEVELOPER IS FLOATED ON THE SURFACE OF SAID CONDUCTIVE LIQUID.
 2. In the process as set forth in claim 1, whereby the developer is floating on the surface of the conductive liquid in a vehicle, the vehicle for said developer being air.
 3. In the process as set forth in claim 1, whereby the developer is floating on the surface of the conductive liquid in a vehicle, the vehicle for said developer being a dielectric liquid.
 4. In the process as set forth in claim 1, the developer interposed between the conductive liquid and the latent image has a thickness of about several hundred microns to several millimeters.
 5. In the process as set forth in claim 1, the conductive liquid is selected from the group consisting of mercury, an aqueous solution or water.
 6. In the process as set forth in claim 1, where the conductive liquid is mercury, the carrier particles are selected from the group consisting of glass particles, plastic particles or ceramic particles.
 7. In the process as set forth in claim 1, where the conductive liquid is water or an aqueous solution, the carrier particles are selected from the group consisting of polyethylene particles, hollow glass particles or plastic balls.
 8. In the process as set forth in claim 1, the size of the carrier particle is about several tens of microns to several millimeters. 